1. Field of the Invention
This invention pertains to acoustical seismic detectors or geophones and more particularly to enhancing the efficiency of reception by geophones using a specially designed extension or spike in connection therewith.
2. Description of the Prior Art
The acoustical seismic detectors or receivers used for land exploration seismic surveys are known as geophones. The term "acoustic seismic detector" is a generic term that for purposes herein, applies to a receiver suitable for sensing elastic motion in the lithology, including the sensing of compressional and shear wave particle motion. Such geophones are disposed in accordance with the requirements of a particular survey at spaced intervals for reception of seismic source signals as they arrive through the air, directly from the source or sources along the surface of the ground and as refracted and reflected by the lithological character of the subsurface. The received data in the form of acoustical energy or elastic motion is converted to corresponding electrical signals by the element or elements in each geophone for transmission and recording with related data from the source(s) and from other geophones. Finally, the data is processed and interpreted or analyzed to yield information about the subsurface character of the lithology. Typically, this is done to determine if there might be hydrocarbon deposits and, if so, at what depths and in what quantity.
Although surveys vary tremendously in their requirements, it is not uncommon for a particular survey to require dozens of geophones. Further, after the readings are recorded for a first location, the geophones are relocated for taking numerous subsequent readings. It is normal practice in approximately 95 percent of the time that each individual geophone is disposed in its position at or very near the surface, although it is important to obtain close coupling with the ground. This coupling can be accomplished with the use of short extensions or feet on the bottom of the housing, there usually being more than one, that embed from a fraction of an inch up to 3 inches into the earth.
It may be noted that geophones come in a variety of forms. Basically, however, geophones include one or more transducer elements that are primarily sensitive to vertical acoustic motion detection, or to horizontal acoustic motion detection, or in some cases, both.
In some locations, it may be desirable to bury the geophones in order to couple them to more competent material than is found at the surface. Digging holes to plant subsurface geophones is expensive, time consuming and sometimes difficult. Moreover, refilling the holes is likewise expensive and time consuming. Holes left unfilled can be hazardous.
Therefore, it is a feature of the present invention to provide an improved geophone with an attachment suitable for coupling with lithology at a location underneath the earth's surface without having to dig a hole for the geophone.
It is another feature of the present invention to provide an improved extension for a geophone in the form of a specially constructed spike for attaching to the lithology at a location underneath the earth's surface without also attaching to the lithology at intermediate locations between the deep end of the spike and the top end of the spike where the geophone is attached.